This study continues to examine the mechanisms underlying sudden cardiac death and myocardial infarction. Cases of Sudden Death are selected retrospectively and their pathologic status including the sites and stages of infarctions and thromboses, and extent of coronary vessel obstruction determined. Special histopathologic technics are applied to determine evidence of non-infarction myocardial injury and the nature of acute and subacute coronary vessel lesions. The types and times of clinical manifestations during the onset and pre-onset periods are obtained. These data are systematically analyzed to identify associations that may exist among the clinical and pathologic findings. Case selection stresses are not limited to moderate altherosclerotic and non-altherosclerotic heart disease.